Characterization of diblock copolymer interfaces: Energy transfer studies and simulations

This thesis describes fluorescence resonance energy transfer (FRET) experiments on the lamellar and cylindrical structures formed in films of poly(isoprene- b-methyl methacrylate) (PI-PMMA) mixtures in which individual polymers are labeled at the junction with a single dye (donor, D (phenanthryl) or acceptor, A (anthryl)). The interface thickness between the PI and PMMA domains was retrieved from analysis of the donor fluorescence decays. FRET operates over short distances and is insensitive to the waviness of the interface. I performed FRET experiments on two parallel PI-PMMA lamellae, in which the acceptors differed in the orientation of their transition moments with respect to the polymer backbone. Identical values of the interface thickness indicate that the dipole orientation for the energy transfer process in this rigid lamellar system makes an identical contribution to both sets of experiments.; Results of Monte Carlo simulation on symmetric diblock copolymer lamellae show that the diblock copolymer chains have only a moderate tendency to orient themselves perpendicular to lamella interface. Both FRET and simulation results indicate that the local correlation in orientation of the polymer chains in the region of the interface is too small to be detected. Numerical FRET simulations on the simulated diblock copolymer lamellae show a coupling effect between the D-A distance and the dipole orientation of the virtual dyes at the junction of the block copolymer chains. This coupling effect tends to decrease the extent of energy transfer and becomes significant only when the dyes are confined to a restricted geometry whose confining space is small and comparable to the Forster radius. Similar results were also found in other confined geometries such as planes, cylinders and spheres.; In the last chapter of this thesis, I describe self-energy transfer experiments on an immobile 2-Anthryl derivative in PMMA films by the fluorescence anisotropy decay technique. Concentration-dependent depolarization took place and was analyzed in terms of the Forster energy transfer mechanism. Similar experiments were carried out on PI-PMMA lamellae with an A group at the block junction. I also found concentration-dependent depolarization, but we lack a theoretical framework to interpret the results in terms of the interface thickness.